My Head Phone Amp Project

[dirkwright]

Originally Posted by JustFJ

why don't you try "the wire headphone amp" instead? their pcb are avaiable nowon, its better performance than this bad quality pcb

Of course, you realize it is rude to suggest something like this, don't you? Maybe you don't have proper manners. I was merely sharing my project, not asking for advice. If I was asking for advice, I would have clearly said so.

Unless you have seen this PCB in person I doubt you know what you're talking about. It is gold plated everywhere and the holes are through hole plated as well. This kind of chip amp is not rocket science anyway. Also, this circuit has two 49600's per channel, which is way overkill.

Exactly how is "the wire" a better PCB, or do you mean circuit?

[dirkwright]

Originally Posted by gumleguf

Nice work. Great sense of detail for sure... :-)

Thanks! It does take a lot of concentration for me to do this, and yet I'm still not satisfied. I'm waiting on some stuff that I ordered, as well as the time to proceed further.

[dirkwright]

So, I had some time today and made some more progress on the enclosure. The rear panel is done. I installed the two Jensen transformers. I used a type of mu metal self stick thin metal under the transformers as a precaution. I put a larger sheet on the underside of the top panel (not pictured). The volume control is also done now. It works great. I need to lay out the front panel next, as well as drill and tap the 4 heatsinks. I finally got the 4-40 tap and drill set in the mail.

Thanks for the encouragement everyone!

[dirkwright]

I finished the front panel today. I had a serious problem because I pressed too hard on the drill press and the drill bit grabbed the panel and bent it up. I was very upset! It took me a while to hammer it back into something close to the way it was before. Now I know - go easy on the drill press and let the bit take it's time to cut through the metal.

It's very industrial looking, I know, but it's all I'm really capable of right now in my shop with the tools that I have.

Thanks for looking.

[ddietz]

Looks great and nothing wrong with the industrial look.

As for the grabbing bit, always clamp anything to the press table that you can, but I don't see much in the photo to complain about!

[dirkwright]

Originally Posted by ddietz

Looks great and nothing wrong with the industrial look.

As for the grabbing bit, always clamp anything to the press table that you can, but I don't see much in the photo to complain about!

Oh, it was clamped to a piece of wood on the drill press, and both were clamped to that. That's why it surprised me. The drill bit just bent it right up! The paint job they used is pretty tough since I pounded the crap out of it to make it reasonably straight again and the paint only has a few scratches on it.

Thanks for your comments.

[cfcubed]

Originally Posted by dirkwright

I added a high frequency pole in the feedback loop as well as an RC low pass filter on the input.

Would you mind elaborating on the above? Those ebay PCBs caught my eye & curious.
Nice looking project BTW... Combining the electrical & the mechanical (pot drive).

[dirkwright]

Originally Posted by cfcubed

Would you mind elaborating on the above? Those ebay PCBs caught my eye & curious.
Nice looking project BTW... Combining the electrical & the mechanical (pot drive).

I replaced the 100K input resistor with a 220pF capacitor, and bypassed the 20kohm feedback resistor with a 10pF capacitor. Otherwise, this amplifier would be working out to radio frequencies. Since the input is connected to the wiper of a 10kohm potentiometer as a volume control, I didn't see the need for the 100k resistor. The LME49710 has an input bias current of a few nanoamps, so that tiny amount of DC through the pot hopefully won't make any difference.

The 10pF capacitor can be tack soldered on the backside of the board across the resistor.

I may not need the 220pF input capacitor since I'm using input transformers which limit input bandwidth anyway, but it's already soldered up now. I guess it's extra security.

Thanks!

[mnturner]

Great job, looks really good. Love the dual pot solution!

[dirkwright]

Originally Posted by mnturner

Great job, looks really good. Love the dual pot solution!

Thanks! I work on it when I have the time. There's always mistakes to either correct or accommodate... sigh.